U.S. Pat. No. 5,692,472 discloses a method and an arrangement for controlling the torque of a motor vehicle wherein the torque of the drive unit is adjusted in dependence upon operating variables of the drive unit and/or of the motor vehicle. Such an operating variable is, for example, the driver command. In the embodiment described, the drive unit is an internal combustion engine having a torque which is adjusted in dependence upon a torque desired value by influencing the following: the air supply, the ignition angle and the fuel metering. This desired value of torque is formed essentially on the basis of the position of an operator-controlled element such as the accelerator pedal and, if required, additional operating variables such as the engine rpm. Furthermore, and at. least on the basis of the driver command, a maximum permissible torque is formed which should not be exceeded in all operating points. The actual value of the torque of the drive unit is computed on the basis of operating variables such as rpm and load and, if required, while considering the ignition angle and fuel adjustment. According to the known procedure, the maximum permissible torque and the actual torque are compared to each other. If the detected actual torque exceeds the maximum permissible torque, the drive unit is controlled in such a manner that the maximum permissible torque is no longer exceeded.
When structuring the maximum permissible torque values in dependence upon driver command, all possibly occurring additional torques are to be considered for each operating point. One example of these additional torques is, in the idle range for a released accelerator pedal, the highest idle drag torque for a very cold engine inclusive of all disturbance variables from electrical consumers (power steering, et cetera). The increase of the actual torque by torques of this kind must be permitted so that the permissible torque values can be relatively high. On the other hand, the reaction of the vehicle should remain controllable in order to detect an impermissible torque increase as early as possible and to counter the same. If the maximum permissible torque for a warm engine is determined, then the permissible torque is exceeded by the actual torque in overrun operation above the idle range for a very cold engine because, then, the drag torque is significantly higher. In this way, the braking action can increase suddenly, for example, during overrun operation in the first gear.
In the known procedure, a compromise must therefore be found between the availability of the motor vehicle with a very cold engine and the operational reliability of the vehicle and this compromise cannot be solved for all operating cases. The same applies also with respect to additional consumers such as climate control systems, power steering, et cetera which increase the torque of the drive unit and load the drive unit.